1. Field of the Invention
This invention relates to novel pterin derivatives and to a radioimmunoassay (hereinafter "RIA") method for determining pterins using a pterin derivative containing a radioiodinated tyramine moiety as the tracer.
2. Description of the Prior Art
In recent years, it has been found that pterins, such as folic acid, play a role as a coenzyme in amino acid-metabolism. Thid finding led to a concept that the detection of quantitative changes of pterins in a living body could be useful for the diagnosis of various enzyme deficiencies. Recently, the relationship between phenylketonuria and biopterin was reported in Annals of Neurology, Vol. 3, pp. 224-230 (1978), The New England Journal of Medicine, Vol. 299, pp. 673-679 (1978) and Clinica Chimica Acta, Vol. 93, pp. 251-262 (1979). Thus, much interest has been shown in the quantitative change of pterins (2-amino-4-hydroxypteridine derivatives) in the human body.
A bioassay method for the determination of biopterin (i.e., 2-amino-4-hydroxy-6-(L-erythro-1,2-dihydroxypropyl)pteridine) is known, as described in Methods in Enzymology, Vol. 18 B, p. 618 (1971), however, this method is not suitable for practical use, because it requires a comparatively long time to obtain the result. A method for the determination of neopterin (i.e., 2-amino-4-hydroxy-6-(L- or D-erythro-1,2,3-trihydroxypropyl)pteridine) has not yet been proposed, but it may become necessary in future.